The physicochemical properties of ricobendazole (RBZ) were characterized using conventional methods. Solubility in some pharmaceutical solvents, pH-solubility, ionization properties, and lipophilicity are described. The solubility of RBZ in water is 62 mg/mL and very poor in common pharmaceutical solvents, for example, oils (<0.25 mg/ mL in all the tested oils) or ethanol (1.2 mg/mL) and propylene glycol (2.6 mg/mL), and slightly higher in dipolar solvents, DMSO (16.5 mg/mL). U-shaped pH-solubility profile in aqueous solutions indicates RBZ is an ampholyte. pK a values measured by absorbance spectroscopy and pH solubility methods were 3.45 and 3.76 for the basic group and 9.82 and 9.53 for the non-basic nitrogen, respectively. Combination of low pH and surfactant/ co-solvent mixtures also improved solubility. RBZ formed a 1:1 complex with hydroxypropyl-b-cyclodextrin (HP-b-CD) with a binding constant (K 1:1 ) of 311/M 1 . Apparent partition coefficients of RBZ were 14.3-15.2 at pH 6-9 and reduced at higher or lower pH. In conclusion, traditional organic co-solvents, pH-adjustment or complexation (with HP-b-CD) approaches are unlikely to yield sufficient solubility for formulation of RBZ solutions for subcutaneous injection and novel approaches should be considered.